1. Field of the Invention
Embodiments of the invention relate generally to the field of data transfer systems. More particularly, an embodiment of the invention relates to data delivery systems in a hybrid fiber-coaxial network, and methods of delivering data in such systems.
2. Discussion of the Related Art
Prior art point-to-multipoint data delivery systems are known to those skilled in the art. For instance, a conventional point-to-multipoint system utilizes a hybrid fiber-coaxial cable (HFC) network of a cable television network. A HFC network uses optical fiber from a central distribution point (the head-end) to an optical node. Coaxial cable runs from the optical node to the service point pickups of individual subscribers, where it interfaces with the cable modems. FIG. 1 shows a conventional HFC network, originally developed for cable access television (CATV). At the central distribution point of the network (the headend) 100, video signals are received from satellites or other sources, combined with locally originated signals and sent down the optical fibers 101 to optical nodes 102. The signal is then converted to coaxial cables 103 which run to the subscriber premises. The fibers are generally in a star configuration while the coaxial cables follow a tree structure. Originally, HFC networks served as a one-way system to deliver video signals to the customers. The signal is delivered with each assigned a 6 MHz bandwidth in the US and 8 MHz in Europe. The frequency band of cable TV channels is 65-850 MHz. Later, the HFC networks were modified, through the addition of amplifiers 104 and other upgrades into a two-way system for providing internet access to the customers. A cable modem termination system (CMTS) at the headend served as the interface to the internet. The CMTS takes traffic from the group of customers served by it and forwards it to an internet service provider (ISP). The ISP, which may be the CMTS itself, will include servers and routers for assigning IP addresses, and providing the DOCSIS (Data Over Cable Service Interface Specification) protocols, which govern the standards for the 7 layers of the OSI (open systems interconnection). The top 3 layers of the OSI, the application, presentation, and session layers are application specific and are always implemented in user software. The transport layer accepts data from the session layer and segments data for transport. Routers operate on the third layer, the network layer. Generally, the CMTS deals with the bottom three layers, the network, datalink, and physical layers.
A single TV channel is generally allocated for downstream data flowing from the CMTS to each subscriber, where it is demodulated by a cable modem. A CMTS can serve up to 2000 cable modems through a single channel. The speeds are typically 3-50 Mbps depending on the bandwidth and modulation used, and the distance can be up to 100 km. More users can be accommodated by designating extra channels for admission. Upstream data flow, since there tends to be much less demand, is designated a 2 MHz channel, typically in the 5-42 MHz range. The data is multiplexed through time division multiple access (TDMA), with either QPSK or 16-QAM modulation. The CMTS allocated time slots to the different cable modems on the network. Thus all modems share the bandwidth and the downstream data are received by all the modems on the system, each modem filtering out the data it needs by deciphering the destination address in the header of each data packet send by the CMTS.
The existing methods provide much lower data rates or do not provide point-to-multipoint solutions or are over fiber or provide only physical layer or require active components between the optical node and the CPE.
A problem with this technology has been the upper limit on the data transfer rate, which is typically in the 3-50 Mbit/s range. Therefore, what is required is solution that allow for higher data rates while taking advantage of the existing architecture.
One unsatisfactory approach, in an attempt to solve the above-discussed problems involves the incorporation of fiber deeper into the network. Depending on how deep the fiber runs, these architectures are known as fiber-to-the-node (FTTN), fiber-to-the-curb (FTTC), or fiber-to-the-home (FTTH). However, a disadvantage of this approach is the limit of the bandwidth of the current deployments of FTTH, FTTC, and FTTN architectures supported by the current Ethernet passive optical networks (EPON), broadband passive optical networks (BPON), and gigabit passive optical networks (GPON) technologies. Furthermore, fibers using coarse wave division multiplexing (CWDM), if used for FDM analog and QAM signals, suffer from SRS-caused crosstalk between the CWDM wavelengths as well as experiencing high levels of dispersion in the 1550 nm window or anywhere above the OH peak.
Another disadvantage of this approach has been the relatively high cost of driving fiber deeper into the network. Therefore, what is also needed is a solution that meets the above-discussed requirements in a more cost-effective manner.
Another unsatisfactory approach has been the use of active components between the optical node and the customer premises equipment. The disadvantage with this approach is that it requires the integration of overlay nodes in the network architecture, and the active nodes have to be collaborated by other routers. Furthermore, this approach is likewise not cost-effective. Heretofore, the requirements of a faster data transfer rate and higher bandwidth have not been fully met. What is needed is a solution that solves these problems.